ZIP CodesHow ZIP codes work: what the five digits mean
A ZIP code is the five-digit postal code of the United States. ZIP stands for Zone Improvement Plan. The Post Office introduced it on 1 July 1963 so that mail could be sorted faster, first by machines reading the digits.
Reading the digits
- The first digit is a group of states. It starts at 0 in the north-east and rises to 9 in the far west.
- The second and third digits, together with the first, point to a regional mail sorting centre.
- The fourth and fifth digits point to a post office or delivery area served by that centre.
Which states use which first digit
Worked out from the 40,977 codes on this site:
| First digit | States |
|---|---|
| 0 | Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, Vermont |
| 1 | Delaware, New York, Pennsylvania |
| 2 | District of Columbia, Maryland, North Carolina, South Carolina, Virginia, West Virginia |
| 3 | Alabama, Florida, Georgia, Mississippi, Tennessee |
| 4 | Indiana, Kentucky, Michigan, Ohio |
| 5 | District of Columbia, Iowa, Minnesota, Montana, North Dakota, South Dakota, Wisconsin |
| 6 | Illinois, Kansas, Missouri, Nebraska |
| 7 | Arkansas, Louisiana, Missouri, Oklahoma, Texas |
| 8 | Arizona, Colorado, Idaho, Nevada, New Mexico, Texas, Utah, Wyoming |
| 9 | Alaska, California, Hawaii, Oregon, Washington |
A state appears in more than one row where a few of its codes carry a neighbour's first digit. Codes starting with 0 keep the zero: Boston is 02108, not 2108. Spreadsheets often drop that zero, so format the column as text.
ZIP+4
Since 1983 a ZIP code can be followed by a hyphen and four more digits, as in 12345-6789. The extra digits point to a smaller unit such as a city block, an office building or a post office box group. Mail arrives without them; they only help sorting. Web forms that ask for a "ZIP code" normally want the first five digits.
ZIP codes are routes, not borders
A ZIP code is a set of delivery routes, not an area with official borders. It can cross city and county lines, and some codes belong to one building, one company or a set of post office boxes. To count people or measure land, the Census Bureau draws approximate areas called ZIP Code Tabulation Areas. The land areas on this site come from those, which is why codes with no homes on them show no area.
Common questions
Is a ZIP code the same as a postal code or PIN code?
Yes, it does the same job. "ZIP code" is the name used in the United States, "postal code" in most countries, and "PIN code" in India.
How many digits does a ZIP code have?
Five. The longer ZIP+4 form has nine digits with a hyphen after the fifth.
Can two towns share one ZIP code?
Yes. A code follows delivery routes, so it can serve several small towns, and a big city has many codes.
Checked in November 2026. General information; this site is not connected with the United States Postal Service.